Polyaniline is the most studied inherently conducting polymer (ICP) because it is inexpensive and relatively easy to synthesize. Polyaniline, however, is limited by its processability [Gregory, Richard V., Chapter 18: Solution Processing of Conductive Polymers: Fibers and Gels from Emeraldine Base Polyaniline in Handbook of Conducting Polymers, Eds. Skotheim, Terje A.; Elsenbaumer, Ronald L.; Reynolds, John R.; Marcel Dekker Inc., (1998) p. 437.]. Lignosulfonic acid-doped polyaniline (ligno-pani), however, is processable due to the grafting of polyaniline onto lignosulfonic acid, which is highly soluble in water [Viswanathan, T., xe2x80x9cConducting Compositions of Matterxe2x80x9d, U.S. Pat. No. 5,968,417 (1999); and Sudhakar, M. et al. Chapter 6. Conducting Waterborne Lignosulfonic Acid-Doped Polyaniline in Semiconducting Polymers, eds. Hsieh, Bing, R.; Wei Yen; American Chemical Society, (1999) p. 76. ]. Only recently has magnetic conducting polyaniline been reported. The most common method of making magnetic polyaniline involves incorporating iron oxide crystals (such as Fe2O3 [Tang, Ben Zhong et al., Chem. Mater. (1999) 11, 1581] or Fe3O4 [Wan, M. et al., J. Polym. Sci. Part A. 1998. 36. 2799]) into the conducting material [Kambe et al., U.S. Pat. No. 5,938,979 (1999)]. These methods, however, require use of organic solvents and the expensive process of laser pyrolysis to form the iron oxide particles. Furthermore, the Fe3O4 ferromagnetic nanoparticles incorporated in the polyaniline decompose when exposed to the strong acids used to dope the polymer. This is a major problem since most conducting polymers need to be doped with strong acids such as hydrochloric acid in order to make them conductive. Another problem is the difficulty of sythesizing complex co-polymers [Fan, J. et al., Solid State Commun. (1999) 110, 57]. Finally, pure polyaniline polymers doped with ferromagnetic material [Wan, M. et al., J. Polym. Sci. Part A. (1998) 36, 2799] is likely not processable due to the limited dispersibility of polyaniline in aqueous solvents and water-soluble resins.
There is currently a need for ferromagnetic conducting polymers which are dispersible in water-soluble resins, inexpensive to synthesisize, and stable in acid.
The present invention provides a conducting ferromagnetic material of the invention comprising ferromagnetic iron oxide particles and a conducting polymer comprising lignosulfonic acid-doped polyaniline. The material of the invention has the advantage of being easily and inexpensively synthesized by dispersing iron cations in aqueous solvents comprising the conducting polymers. In addition, the iron oxide particles in the materials of the invention have improved acid stability compared to the iron oxide particles incorporated in polyaniline polymers. The conducting polymer component of the invention also has the advantage of being easily synthesized from common and inexpensive starting materials. The conducting ferromagnetic material of the present invention also has the advantage of being dispersible in aqueous solvents or water-based resins. This makes the materials more easily processable and helps to minimize pollution from the use of organic solvents.
The invention provides a conductive ferromagnetic composition of matter comprising: (a) linearly conjugated xcfx80-systems; (b) residues of sulfonated lignin or a sulfonated polyflavonoid or a derivative of a sulfonated lignin or a sulfonated polyflavonoid; and (c) ferromagnetic iron oxide particles.
The invention further provides a barrier to electromagnetic radiation comprising: (a) linearly conjugated xcfx80-systems and residues of sulfonated lignin or a sulfonated polyflavonoid or a derivative of a sulfonated lignin or a sulfonated polyflavonoid; and (b) ferromagnetic iron oxide particles.
The invention further provides an apparatus comprising: a substrate; and a ferromagnetic layer on the substrate, wherein the ferromagnetic layer comprises (a) linearly conjugated xcfx80-systems; (b) residues of sulfonated lignin or a sulfonated polyflavonoid or a derivative of sulfonated lignin or a sulfonated polyflavonoid; and (c) iron oxide particles.
The invention further provides a method of shielding an article from electromagnetic radiation; comprising the step of interposing an electromagnetic shielding material between the article and one or more sources of electromagnetic radiation; the electromagnetic shielding material comprising: (a) linearly conjugated xcfx80-systems; (b) residues of sulfonated lignin or a sulfonated polyflavonoid or a derivative of sulfonated lignin or a sulfonated polyflavonoid; and (c) ferromagnetic iron oxide particles.
The invention further provides a method for preparing a conductive ferromagnetic composition of matter comprising combining (1) a polymer comprising (a) linearly conjugated xcfx80-systems, and (b) sulfonated lignin or a sulfonated polyflavonoid or a derivative of sulfonated lignin or a sulfonated polyflavonoid; and (2) a source of ferromagnetic iron oxide particles.
The invention further provides a conductive ferromagnetic composition of matter formed by a process comprising combining (1) a polymer comprising (a) linearly conjugated xcfx80-systems, and (b) sulfonated lignin or a sulfonated polyflavonoid or a derivative of sulfonated lignin or a sulfonated polyflavonoid; and (2) a source of ferromagnetic iron oxide particles.
The invention further provides a method of forming a conductive ferromagnetic composition of matter comprising: combining in a mixture (1) a polymer comprising (a) linearly conjugated xcfx80-systems, and (b) sulfonated lignin or a sulfonated polyflavonoid or a derivative of sulfonated lignin or a sulfonated polyflavonoid; and (2) ferrous ions; and (3) an aqueous solvent; and adding a base to adjust the pH of the mixture to at least about 7.
The invention further provides a conductive ferromagnetic composition of matter formed by a process comprising: combining in a mixture (1) a polymer comprising (a) linearly conjugated xcfx80-systems, and (b) sulfonated lignin or a sulfonated polyflavonoid or a derivative of sulfonated lignin or a sulfonated polyflavonoid; and (2) ferrous ions; and (3) an aqueous solvent; and adding a base to adjust the pH of the mixture to at least about 7.
The conducting ferromagnetic compositions of the present invention can be used for many purposes. They can be used, for example, as barriers to absorb or filter electromagnetic radiation. They can be used as electronic data storage materials. They can also be used as coatings to protect metals against corrosion, as described in U.S. patent application Ser. No. 09/903,260, which is hereby incorporated by reference. They can also be used as anti-static coatings or components of fibers and fabrics as disclosed in U.S. Pat. No. 6,059,999, which is hereby incorporated by reference.